Dual curing silicone compositions

ABSTRACT

The present invention relates to dual curing silicone compositions which are capable of cross-linking when subjected to ultraviolet (“UV”) or visible (“VIS”) light and/or by a moisture condensation method. When cured, these compositions have excellent adhesion to a variety of substrates. These are particularly useful in potting and coating applications.

This application claim the benefit of provisional application No.60/090,403 filed Jun. 24, 1998.

FIELD OF INVENTION

The present invention relates to dual curing silicone compositions whichare capable of cross-linking when subjected to radiation in theultraviolet (“UV”) or visible (“VIS”) regions of the electromagneticspectrum, and/or by a moisture condensation method. When cured, thesecompositions have excellent adhesion to a variety of substrates. Theyare particularly useful in potting and coating applications.

BRIEF DESCRIPTION OF THE RELATED TECHNOLOGY

Silicone rubber and liquid compositions exist in various forms and theircharacteristics may be modified to impart specific characteristics suchas cure chemistry, viscosity, polymer type and purity. They can beformulated into one-part or two-part systems and a particular siliconecomposition can be engineered to be cured by more than one mechanism.Moisture-curing mechanisms, heat-curing mechanisms, and photoinitiatedcuring mechanisms are among those mechanisms used to initiate cure,i.e., cross-linking of reactive silicones. These mechanisms are based oneither condensation reactions, whereby moisture hydrolyzes certaingroups on the silicone backbone, or addition reactions which can beinitiated by a form of energy, such as electromagnetic radiation orheat. For example, reactive polyorganosiloxanes can be cured by heat inthe presence of a peroxide, or they can be cured by heat in the presenceof a silicon hydride-containing (SiH) compound and a metallichydrosilylation catalyst, such as an organo-platinum catalyst.

Typically, moisture curable materials are manufactured by endcappingα,ω-silanol terminated silicones with various crosslinkers such asalkoxysilanes, oximinosilanes, acetoxysilanes, aminosilanes, and othersilanes with hydrolyzable groups attached to the silicon atom(s)thereof. The resulting silicone materials are stored in moistureimpermeable containers.

During application to a respective substrate, the materials are extrudedor otherwise applied and exposed to ambient conditions for curing. Themoisture in the air then will hydrolyze the hydrolyzable groups (such asalkoxy, oximino, acetoxy, and amino) on the silicon atom(s) to formsilanol, either with or without inclusion of a catalyst. The resultingsilanol can then further react with remaining unhydrolyzed groups in acondensation reaction, to form a siloxane linkage resulting in the cureof the silicone material.

Although these materials when cured are very reliable and possesssuperior properties as coatings, the moisture cure tends to be slow.Cure times of 24 hours or more may often be needed before a full curecan be achieved. Such cure times limit through-put in the manufacture ofcoated components, since full cure of the coated components is neededbefore the components can be used in the next step of the manufactureprocess.

As a result, a third curing mode, ultraviolet light curing, has gainedwide acceptance in recent years. The curing is relatively fast, with thecured elastomer showing good adhesion to the substrates. In situationswhere portions of the coated material are shaded during the UV cure, asecondary cure mode, usually moisture cure can be further incorporated.

Typically, UV cure of silicone compositions can be achieved by either athiol-ene cure or by an acrylate cure. In the thiol-ene cure, a thiolfunctional silicone is reacted with a vinyl functional silicone. Thecure is fast and the surface dry to the touch upon the completion of thecure. However, it has been reported that in commercial applications thecured product does not heat age well, and the uncured composition tendsto lack long-term storage stability.

On the other hand, acrylate functional silicone is usually storagestable and the cured products exhibit excellent high temperatureresistance. However, with an acrylate cure in the presence ofatmospheric oxygen, the surface cure tends to be incomplete and thecured product often times tends to be tacky.

Dual-curing silicone compositions using UV light and moisture curingmechanisms are disclosed in U.S. Pat. No. 4,528,081 (Lien) and U.S. Pat.No. 4,699,802 (Nakos). These patents disclose compositions particularlyuseful for conformal coatings in electronic applications where thesubstrate has shadow areas which are not readily accessible to direct UVlight and require moisture cure for cross-linking of those areas.Ordinarily, in addition to the photoinitiator present for radiationpolymerization, a moisture curing catalyst such as an organotitanate ororganotin is present. Without the moisture curing catalyst, moisturecure does not ordinarily take place with any degree of certainty or inany predictable time frame. Thus, as a practical matter, without themoisture curing catalyst, the moisture curing aspect of thesecompositions would not be practical for commercial use.

U.S. Pat. No. 4,587,173 (Eckberg) discloses dual curing siliconecompositions using heat and UV light as separate cross-linkingmechanisms. This patent discloses a reactive polyorganosiloxane whichrequires direct silicon-bonded hydrogen atoms and direct silicon-bondedalkenyl radicals on the same or different polysiloxane chains. Thesecompositions also contain a photoinitiator and a preciousmetal/hydrosilation catalyst. The presence of the photoinitiator allowscross-linking of the silicon-bonded hydrogen atoms and silicon-bondedalkenyl radicals. These compositions are said to be able to cross-linkat room temperature or at elevated temperatures by the precious metalcatalysis of the silicon-bonded hydrogen atoms and silicon-bondedalkenyl radicals. Platinum is among the catalysts used for the thermalhydrosilation cure reaction. Moreover, this patent requires a peroxide,which can decompose over time even at room temperature and thereby limitshelf-life.

U.S. Pat. No. 4,603,168 (Sasaki) discloses a method of curingorganopolysiloxane compositions, which requires the use of heat incombination with ultraviolet radiation. These compositions contain anorganopolysiloxane having per molecule at least two alkenyl groupsbonded directly to the silicone atom. Other organic groups may also bepresent, such as alkyl groups, halogenated alkyl groups, aryl groups,aralkyl groups, and alkaryl groups on the organopolysiloxane backbone.In addition, an organohydrogenpolysiloxane containing at least twoorganohydrogensiloxane or hydrogensiloxane units per molecule, aplatinum catalyst, an addition-reaction retarder and a photoinitiatorare also disclosed. The alkenyl groups must be bonded directly to thesilicone atom without an organo group therebetween. Both the '173 and'168 patents are also limited to very thin coatings.

Dual-curing compositions employing UV- and moisture-cure mechanisms havea basic disadvantage in that once exposed to ambient moisture, theybegin to cure. In many cases, this results in premature curing andshortened shelf life, as well as pot life in use. The advantage of themoisture cure mechanism is that it provides a means to cure shadow areasblocked from UV light. This is particularly important when hightemperature curing is not an acceptable commercial option due, forinstance, to the heat sensitivity of the substrate to which the reactivesilicone is applied. For example, in conformal coatings where thesubstrate is an electronic circuit board, high temperature curingsystems such as those which use peroxides, are not practical.Conventionally, moisture, UV, heat or combinations thereof have beenemployed as curing mechanisms for such applications.

More recently, as disclosed in the '173 and '68 patents discussed above,heat and UV curing mechanisms have been combined. While these patentsdisclose compositions which may be useful for heat sensitive substratesdue to the combination of UV and low temperature heat cure, eachrequires a specific type of organopolysiloxane. In the '173 patent, thepolyorganosiloxane backbone contains both a hydrogen atom bonded to asilicon atom in the backbone, as well as an olefinic group bonded to asilicon atom. In the '168 patent, the polyorganosiloxane contains analkenyl group bonded directly to a silicone atom.

U.S. Pat. No. 5,179,134 (Chu) and U.S. Pat. No. 5,212,211 (Welch, II)describe acryloxy functional capped silicones. The silicones of the '134patent cure only through a photoinitiated mechanism, whereas thesilicones of the '211 patent cure through such a mechanism, as well asthrough a second mechanism, such as moisture or heat, by virtue ofadditional functional groups attached to the siloxane backbone.

U.S. Pat. No. 5,498,642 (Chu) discloses a dual curing siliconecomposition, which uses a vinyl dialkoxysilyl-terminatedpolydimethylsiloxane polymer to provide both UV and moisture curing.This polymer provides better surface skinning during UV exposure,largely due to the presence of the vinyl group, which serves to helpeliminate tackiness. Further curing of the composition beneath theUV-formed skin occurs over time through a moisture curing mechanism.

U.S. Pat. No. 5,516,812 (Chu) also discloses a radiation andmoisture-curable silicone composition. This composition also employs asilicone endcapped with vinyl functionality in combination with a secondsilicone fluid having radiation and moisture curable groups present.This composition is specifically designed for conformal coatingcompositions having improved surface tack.

Notwithstanding the state-of-the-art, it would be desirable to provide adual UV-curable, moisture-curable silicone composition where cure of thecomposition by UV results in a coating that is dry to the touch withoutthe common tacky surface often associated with an acrylate cure. Itwould also be desirable to provide such compositions having at least twodifferent siloxanes, one of which has the ability to photocure and theother of which has the ability to both photocure and cure throughexposure to moisture.

SUMMARY OF THE INVENTION

The present invention provides compositions which cure through aphoto-initiated mechanism and a dual photo-initiated moisture-curingmechanism. That is, at least two different functionally-terminatedpolyorganosiloxanes are present in the inventive composition. In aparticularly desirable aspect of the present invention, three of suchdifferent functionally terminated polyorganosiloxanes are present. Thesecompositions are specifically designed to be curable by exposure toactinic radiation and/or moisture.

In one aspect, the invention provides a radiation and moisture-curablesilicone composition that includes:

(A) a silicone fluid comprised of a monovalent ethylenically unsaturatedfunctional group capped silicone capable of UV and moisture curing:

(B) a (meth)acryloxy-functional capped silicone fluid capable of UVcuring, wherein the (meth)acryloxy-functional capped silicone fluid isformed as a reaction product of: (i) a silyl di(meth)acrylate compoundof the formula:

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ are independentlyselected from the group consisting of hydrogen, halo, and organoradicals; and n is an integer having a value of from 1 to 4; and (ii) asilicone having at least one functionality which is reactive with a(meth)acryloxy functionality of said silyl di(meth)acrylate compound toyield said (meth)acryloxy-functional capped silicone;

(C) a photoinitiator effective for radiation curing of the siliconecomposition; and

(D) a moisture curing catalyst.

The capped silicone of (A) is the product of a reaction between asilanol-terminated silicone and a silane having a monovalentethylenically unsaturated functional group and at least 2 hydrolyzablegroups. The (meth)acryloxy-functional capped silicone of (B) is theproduct of a reaction between a silanol-terminated silicone and a silanehaving a (meth)acrylate and at least 2 hydrolyzable groups.

In the particularly desirable aspect noted above, the present inventionprovides compositions that include the silicones of (A) and (B), as wellas a third silicone (E), which includes at least one(meth)acryloxydimethoxyalkyl-terminated polyorganosiloxane.

In another aspect, the present invention provides compositions thatinclude:

(i) a first silicone which is capped with vinyl functionality and is thereaction product of a silanol-terminated silicone having at least 60mole percent Si—OH terminated groups, and has a viscosity at roomtemperature of greater than 1,000 cps, desirably 1,500-10,000 cps, and asilane having at least one vinyl group and at least two hydrolyzablefunctional groups [such as the silane having a monovalent ethylenicallyunsaturated functional group and at least 2 hydrolyzable groupsdescribed for silicone (A)];

(ii) a second silicone fluid having radiation-curable (meth)acrylfunctional groups as described above; and

(iii) an effective amount of a photoinitiator.

These compositions may also include a moisture cure catalyst.

The inventive compositions are particularly advantageous when used inpotting applications, or as coatings for electronic applications,particularly those which are temperature sensitive.

The present invention provides an improvement over known dual curesilicone compositions, which depend primarily on siloxanes having the UVand moisture cure capabilities on the same polyorganosiloxane for cure,by providing compositions that include separate polyorganosiloxanes, afirst of which depends primarily on vinyl groups for photocure andmoisture, and a second of which depends on both (meth)acrylatephotocuring groups for photocure. By providing separatepolyorganosiloxanes in this manner, the composition can be tailored forspecific desired characteristics by balancing the proportions of onepolyorganosiloxane with respect to the other polyorganosiloxane. Thepresent invention allows for enhanced UV cure capability, particularlyat the surface, in a relatively short time frame, as well ascompleteness of cure—or cure through volume—by virtue of the moisturecure mechanism and/or the UV cure mechanism.

The inventive compositions once cured provide cured elastomers havingimproved adhesion to a variety of substrates and by-products which arenon-corrosive.

Moreover, the present invention does not suffer from the limitation ofbeing for use as thin coatings, as described by the '173 and '168patents previously discussed, and either cure mechanism can be used tocure a range of thicknesses, for example, up to 50 mm or more. Certainof the benefits and advantages of the present invention are believed tobe attributed to the specific combination of siloxanes andphotoinitiators and moisture cure catalysts, which will become morereadily apparent from a reading of the sections entitled “DetailedDescription of the Invention” and “Examples”, which follow.

DETAILED DESCRIPTION OF THE INVENTION

The ethylenically unsaturated functional group capped silicone (A) usedin the inventive compositions is formed as the reaction product of asilanol terminated silicone and a silane having a monovalentethylenically unsaturated functional group and at least two hydrolyzablegroups. These silicones are disclosed in U.S. Pat. No. 5,498,642 (Chu),the disclosure of which is hereby expressly incorporated herein byreference.

The silanol terminated silicone used to make silicone (A) should includea linear polydiorganosiloxane having a viscosity as measured on aBrooksfield viscometer at ambient temperature (about 25° C.) of morethan 1,000 centipoise (“cps”), desirably between 2,000 and 10,000 cps,such as between 2,000 and 5,000 cps.

This silicone is ordinarily a predominantly linear structure incharacter, having the silanol (—SiOH) functionality located at theterminus of a polysiloxy [—(SiO)_(x)—] moiety in the silicone molecule.

The silane which reacts with the silanol capped silicone may bedescribed with reference to the formula: R_(a)SiX_(b), where each R isindependently selected from monovalent ethylenically unsaturatedradicals, hydrogen, C₁₋₈ alkyl, C₆₋₁₂ aryl, C₇₋₁₈ arylalkyl, C₇₋₁₈alkylaryl, and X; X is a monovalent functionality imparting moisturecurability to the reaction product of the silanol-functionalizedsilicone and silane crosslinker; a has a value of 1 or 2; b has a valueof 2 or 3; and a+b=4, provided that when a is 1, R is a monovalentethylenically unsaturated radical, and that when a is 2, at least one Ris a monovalent ethylenically unsaturated radical.

Thus, R may be a monovalent ethylenically unsaturated radical forexample, selected from the group consisting of vinyl, propenyl, butenyl,pentenyl, hexenyl, octenyl, allyl, alkenyloxy, alkenylamino, allyloxy,allylamino, furanyl, phenyl and benzyl groups. Examples includevinyltrimethoxysilane, vinyltriminosilane, vinyltriisopropenyloxysilaneand vinyltriacetoxysilane.

The monovalent ethylenically unsaturated functional group cappedsilicone (A) may be present in amounts of about 5 to about 60% byweight, desirably in amounts of about 15 to about 40% and more desirablyabout 20 to about 35% by weight. This component provides UV surfacecuring and moisture curing throughout the thickness of the inventivecomposition.

The (meth)acryloxy-functional capped silicones (B) of the presentinvention are formed as a reaction product of a silanol terminatedsilicone and a silane having a (meth)acrylate and at least twohydrolyzable groups. These (meth)acryloxy-functional capped siliconesare set forth in detail in U.S. Pat. No. 5,212,211 (Welch, II), thedisclosure of which is hereby expressly incorporated herein byreference.

The acryloxy-functional capped silicone fluid (B) is formed as areaction product of:

(i) a silyl di(meth)acrylate compound of the formula:

 wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ are independentlyselected from the group consisting of hydrogen, halo, and organoradicals; and n is an integer having a value of from 1 to 4; and

(ii) a silicone having at least one functionality which is reactive witha (meth)acryloxy functionality of said silyl di(meth)acrylate compoundto yield said (meth)acryloxy-functional capped silicone. This siliconereactive with the silyl di(meth)acrylate may impart a curing mechanismother than photocuring. Desirably, this silicone imparts moisture curingdue to the presence of one or more of the following moieties which canundergo hydrolysis and which are selected from the group consisting ofhydroxyl, enoloxy, amino, alkoxy, aryloxy, oxime, N,N-dialkylamino, N,N-dialkylaminoxy, N-alkylamido,O—C(CH₃)═CH₂,—S—C₃H₆Si(OCH₃)₃,—O—NH—C—(O)—H and combinations thereof.

The (meth)acryloxy-functional capped silicone (B) may be present inamounts of about 5 to about 90% by weight, desirably about 30 to about70% and more desirably about 40 to about 60% by weight. This componentprovides UV curing throughout the thickness of the inventivecomposition.

The (meth)acryloxyalkyldialkoxy-terminated polyorganosiloxanes (E) thatmay be included in certain aspects of the present invention include atleast one terminal alkoxy group, and desirably two reactive functionalgroups. Such a material is a product of the reaction of anorganopolysiloxane, having at least one end (and desirably both ends)terminated with a silanol group, with a silane containing at least two(and desirably three) alkoxy groups. The number and type of functionalgroup(s) present can be varied according to the desired properties ofthe final silicone composition. Due to the presence of these functionalgroups on (E) and the presence of silicones (A) and (B) referred toabove, these compositions can be initially cured on a surface byexposure to actinic radiation through a photoinitiated mechanism tothicknesses considerably greater than compositions known heretofore, andmore fully cured at ambient temperature in the presence of moisture.

For purposes of this invention, the term “actinic radiation” is meant toinclude particle or wave electromagnetic radiation and photochemicalradiation.

The ability to cure tack free through a photo-induced mechanism througha variety of thicknesses, for example, from about 0.1 mm up to about 50mm, allows for a variety of potting and/or coating applicationsheretofore not permitted by other potting compositions using UV curingmechanisms. For example, the '178 patent either does not cure or onlypartially cures at thicknesses of 8 mm. (See Table 1, col. 10.)Moreover, the '168 patent uses one gram per square meter of thiscomposition as a coating, presumably due to the inability to ordifficulties in cure at greater thicknesses. Thus, the advantagesobtained by the specific functional groups on the polyorganosiloxanebackbone of the present invention are readily apparent. In addition, asnoted herein, the use of moisture cure catalysts, such as titanates,which do not absorb appreciable amounts of actinic radiation provide theability to cure to greater thicknesses as the moisture cure catalystused in the present invention does not compromise the ability of thecomposition to cure under exposure to such radiation.

The (meth)acryloxyalkyl-terminated polyorganosiloxane (E) desirablyshould be in accordance with formula I below:

wherein R¹, R², R³ and R⁴ may be the same or different and aremonovalent hydrocarbon radicals having up to 10 carbon atoms (C₁₋₁₀) orhalo or cyano substituted hydrocarbon radicals; R³ may also be amonovalent heterohydrocarbon radical having up to 10 carbon atoms(C₁₋₁₀) where the hereto atoms are selected from halo atoms, O, N, andS; R⁵ is alkyl (C₁₋₁₀), such as methyl, ethyl or isopropyl; providedthat at least one R³ or a terminal end is a (meth) acryloxyalkyl group;R⁵ may also include an ether linkage, such as CH₂CH₂OCH₃; n is aninteger; a is 0, 1 or 2; b is 0, 1 or 2; and a+b is 1 or 2.

The number of repeating units in the reactive polyorganosiloxanes can bevaried to achieve specific molecular weights, viscosities and otherchemical or physical properties. Generally n is an integer such that theviscosity is from about 25 cps to about 2,500,000 cps at 25° C., such aswhen n is from 1 to 1,200 and desirably from 10 to 1,000.

Component (E) may be present in amounts sufficient to provide enhancedUV and moisture curing capability. Desirably (E) is included in amountsof about 5 to about 70% by weight and more desirably about 5 to 25% byweight.

A particularly desirable silicone fluid for (E) has the followingformula II where R³ on formula I is a methacrylate-propyl group,CH₂C(CH₃)—COOC₃H₆, R⁴ and R⁵ on formula I are methyl, and R¹ and R² areas described in formula I above to give:

where MA is the methacryloxypropyl group, n is from 1 to 1,200, a is 1and c is 0 or 1.

The functional terminated polyorganosiloxanes of the present inventionmay be present in combined amounts of about 5 to about 95%, such asabout 30 to about 70% by weight, desirably about 40 to about 60% byweight.

Due to the presence of both alkoxy and vinyl groups, and desirablyalkoxy, vinyl and acrylate groups, these compositions are capable ofcuring by both moisture and photo curing mechanisms. Thus, for example,the inventive compositions can be subjected to UV light in the presenceof a photoinitiator to partially cure or gel the material, which canthen be allowed to cure further by moisture in ambient conditions.

The number of repeating units in the polyorganosiloxanes can be variedto achieve specific molecular weights, viscosities and other chemical orphysical properties. Generally, n is an integer such that the viscosityis from about 25 cps to about 2,500,000 cps at 25° C., such as when n isfrom 1 to 1,200 and desirably from 10 to 1,000.

The photoinitiators useful in the present invention may be selected fromany known free radical type photoinitiator effective for promotingcrosslinking reactions. For example, suitable photoinitiators include UVinitiators such as benzophenone and substituted benzophenones,acetophenone and substituted acetophenones, benzoin and its alkylesters,xanthone and substituted xanthones. Desirable photoinitiators includediethoxyacetophenone (DEAP), benzoin methyl ether, benzoin ethyl ether,benzoin isopropyl ether, diethoxyxanthone, chloro-thioxanthone,azo-bisisobutyronitrile, N-methyl diethanolaminebenzophenone, andcombinations thereof.

Visible light photoinitiators include camphoquinone peroxyesterinitiators, non-fluorene carboxylic acid peroxyester initiators andalkyl thioxanthones, such as isopropyl thioxanthone.

While the photoinitiator may be present in any effective amount,desirable ranges include about 1 to about 10% by weight, such as about 2to about 6% by weight. A particularly desirable photoinitiator is DEAP.

The compositions also include moisture curing catalysts to enhance therate at which the hydrolyzable groups on the polyorganosiloxane reactwith moisture to cure. Such hydrolyzable groups include amino, oxime,acetoxy, alkoxy, aryloxy, alkaryloxy, aryalkoxy and the like. Where thehydrolyzable groups are amino, oxime or acetoxy, however, moisture curemay occur fast enough such that a moisture catalyst may not benecessary.

The moisture curing catalysts include organo-metal catalysts includingtitanates such as tetraisopropylorthotitanate andtetrabutoxyorthotitanate, as w ell a s metal carboxylates such asdibutyltin dilaurate, dibutyltin dioctoate and the like.

The moisture cure catalyst should be used in an amount sufficient toeffectuate moisture cure, which desirably is in the range of about 0.1to about 5% by weight.

Useful UV radiation sources include conventional mercury-vapor lampsdesigned to emit ultraviolet energy in various ultraviolet wavelengthbands. For example, useful radiation wavelength ranges include 220 to400 nm.

It should be understood that while the photoinitiator is generally usedas a separate component, the formulations used in the inventivecomposition are intended to include those in which photoinitiatinggroups are included in the backbone of the same organopolysiloxanepolymer which includes the photocuring groups.

The inventive compositions may also contain other additives so long asthey do not interfere with the curing mechanisms. For example,conventional additives such as fillers, adhesion promoters, pigments,moisture scavengers, inhibitors and the like may be included.

Fillers such as fumed silica or quartz are contemplated , as aremoisture scavengers such as methyltrimethoxysilane and vinyltrimethoxysilane. Fillers may be present in amounts up to about 30% byweight, such as about 4 to about 20% by weight.

Inhibitors may be present up to about 10% by weight, desirably about 0.5to about 1% by weight. The particular amount of inhibitor should bebalanced in a given composition to produce or improve stability of thecomposition.

Adhesion promoters may be present in amounts of up to about 5%, such asabout 2% by weight.

UV cure is generally effected in the range of 40 milliwatts/cm²(“mW/cm²”) to about 300 mW/cm², such as in the range of about 70 mW/cm²to about 150 mW/cm².

As an alternative aspect of the invention, heat curing may be used tocure the compositions, provided a heat cure catalyst, such as platinum,is used, and at least one of the polyorganosiloxanes includes a hydrideterminal group available for condensation with the ethyleneicallyunsaturated group on another of the polyorganosiloxanes. For example,room temperature cure is contemplated, as well as temperatures up toabout 150° C., such as in the range of from about 65° C. to about 125°C. and desirably in the range of from about 85° C. to about 100° C.Although heat curing can be effected at higher temperatures than thesegiven, the recited temperatures allow for use of the compositions inapplications, such as potting applications and coatings for electronicapplications, which are temperature sensitive.

The compositions of the present invention may be prepared by mixingtogether the respective components to obtain a substantially homogenousor uniformly blended material and stored in containers which arenon-transmissive to UV light and moisture. Generally, a single packagesystem is employed, but two-part package systems may be used if desired.Whereas single package products are ready-for-use upon being dispersed,two-part systems require mixing of the dispersed parts prior to use.

The inventive compositions may be used as noted above in pottingapplications and coatings for a variety of substrates includingelectronic parts and other heat-sensitive materials.

The following examples are provided for illustrative purposes only, andare in no way intended to limit the scope of the present invention.

EXAMPLES

In these examples, percent weights are per the total composition unlessotherwise specified.

The vinyldimethoxy-terminated polydimethylsiloxane polymers used in thepresent invention were made in accordance with the teachings of U.S.Pat. No. 5,498,642. Accordingly, two hundred fifty seven grams of the3,500 cps silicone fluid was allowed to react with 3.0 grams ofvinyltrimethoxysilane in the presence of 0.2 ml of butyllithium (1.6 M)in a reaction vessel with nitrogen sparge for 90 minutes and thensparged with carbon dioxide for 30 minutes to obtain avinyldimethoxysilyl-terminated silicone fluid.

The acryloxymethyldimethylsilyl-terminated polydimethylsiloxane polymersused in the present invention were made with the teachings of U.S. Pat.No. 5,212,211. Accordingly, 2 moles (about 500 grams) ofacryloxymethyldimethylacryloxysiloxane was reacted with 12 kg of 750 cps(m.w. 12,000) silanol fluid at room temperature, followed by strippingto remove the acrylic and by-product. The resultant polymer wasacryloxymethyldimethylsilyl-terminated polydimethylsiloxane.

The methacryloxyalkyldimethoxy-terminated polydimethylsiloxane polymersused in the present invention were made in accordance with the teachingsof U.S. Pat. No. 5,300,608. Accordingly, 500 grams of a 2,000 cps(spindle #4) silanol-terminated polydimethylsiloxane fluid was placed ina reaction vessel. Fourteen grams of methacryloxypropyltrimethoxysilanewas then added. To this mixture, with stirring, was further added 0.65grams of lithium n-butyldimethylsilanolate solution previously prepared.The mixture was stirred at room temperature under nitrogen for 3 hours.The temperature of the mixture rose to 50° C. due to shearing. A gentlestream of carbon dioxide was bubbled into the system for 10 minutes forcatalyst quenching. The mixture was then heated to 110° C. undernitrogen sparge for 30 minutes to remove volatile materials. At roomtemperature, the mixture showed a viscosity reading of 3,100 cps(Brookfield Viscometer, spindle #4 at 10 rpm).

Table I represents compositions in accordance with the present inventionwhich contain three reactive silicone polymers as well as thephotoinitiator, moisture cure catalyst and other useful additives. Thedesired ranges of the components are provided.

TABLE I Range Component (Wt %) Vinyldimethoxy-terminated 18-32polydimethylsiloxane (m.w. 28,000) Acryloxymethyldimethysilyl-terminated25-55 polydimethylsiloxane (m.w. 12,000)Methacryloxyalkyldimethoxy-terminated  5-60 polydimethylsiloxane (m.w.20,000) Fumed silica (filler) 4.2-4.7 Photoinitiator 2.4-3.6 Moisturecure catalyst 0.3-0.5 Monomer diluent 3.7-6.3 Adhesion promoter1.75-4.25 Vinyl trimethoxysilane (crosslinker) 2-3 Dye 0.003-0.008

TABLE II Composition Wt % Component A B C D E Vinyldimethoxy-terminated26.0 27.6 27.6 19.63 43.3 polydimethylsiloxane (m.w. 28,000)Acryloxymethyldimethylsilyl-ter- 52.8 55.2 55.2 54.56 43.3 minatedpolydimethylsiloxane (m.w. 12,000) Photoinitiator 2.8 2.0 2.0 3.92 2.0Adhesion promoter 6.7 — — — — Monomer diluent 3.7 — 5.0 3.92 Tincarboxylate (moisture catalyst) 0.2 0.2 0.2 0.3 0.2 Plasticizer/Filler13.9 15 10 17.66 13.2

Compositions A-E were tack free after exposure to UV and furthermoisture curing for a period of 2 hours at room temperature. Thesecompositions, when fully cured after overnight ambient cure showed goodadhesion on the following substrates: nylon, polyoxymethylene acetalresin sold under the trademark Delrin, polyetherimide sold under thetrademark Ultem; and polyethylene terephthalate sold under the trademarkVALOX.

Composition C was also UV cured and ambient cured overnight in sheets of0.035″ thick and subsequently yielded a tensile strength at roomtemperature of 68 psi, a tensile strength at 50% RH of 18 psi, and anelongation at room temperature of 279%. When Composition C was UV curedand room temperature cured for 7 days in sheets of the same thickness,the following results were obtained: room temperature tensile strengthsof 58 psi; a tensile strength of 27 psi at 50% RH; and a roomtemperature elongation of 145%.

What is claimed is:
 1. A radiation and moisture-curable siliconecomposition, comprising: (A) a first silicone fluid, said first siliconefluid comprised of a monovalent ethylenically unsaturated functionalgroup endcapped silicone, said endcapped silicone being the product of areaction between a silanol terminated silicone and a silane crosslinkerhaving joined directly to a silicon atom thereof a monovalentethylenically unsaturated functional group and at least 2 hydrolyzablegroups; (B) a second silicone fluid, said second silicone fluidcomprised of a (meth)acryloxy-functional capped silicone fluid capableof UV curing, said (meth)acryloxy-functional capped silicone fluid beingformed as a reaction product of: (i) a silyl di(meth)acrylate compoundof the formula:

 wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ are independentlyselected from the group consisting of hydrogen, halo, and organoradicals; and n is an integer having a value of from 1 to 4; and (ii) asilicone having at least one functionality which is reactive with a(meth)acryloxy functionality of said silyl di(meth)acrylate compound (C)a photoinitiator component; and (D) a moisture curing catalyst.
 2. Thecomposition according to claim 1, wherein (i) said first silicone fluidis endcapped with vinyl functionality and is the reaction product of asilanol-terminated silicone having a viscosity at room temperature ofgreater than 1,000 cps, and a silane crosslinker having at least onevinyl group and at least two hydrolyzable functional groups; and (ii)said second silicone fluid includes both radiation-curable (meth)acrylfunctional groups and moisture-curable hydrolyzable groups.
 3. Thecomposition according to claim 2, wherein the mole ratio of vinylfunctional groups to the (meth)acryl functional groups is from 5:95 to4:6.
 4. The composition according to claim 2, wherein said silanecrosslinker is within the formula, R_(a)SiX_(b), wherein R is a memberselected from the group consisting of monovalent ethylenicallyunsaturated radicals, hydrogen, C₁₋₈ alkyl, C₆₋₁₂ aryl, C₇₋₁₈ arylalkyl,C₇₋₈ alkylaryl, and X; X is a monovalent functionality impartingmoisture curability to the reaction product of thesilanol-functionalized silicone and silane cross-linker, a has a valueof 1 or 2; b has a value of 2 or 3; and a+b=4, provided that when a is1, R is a monovalent ethylenically unsaturated radical, and that when ais 2, at least one R is a monovalent ethylenically unsaturated radical.5. The composition according to claim 4, wherein R is a monovalentethylenically unsaturated radical.
 6. The composition according to claim4, wherein R is selected from the group consisting of vinyl, propenyl,butenyl, pentenyl, hexenyl, octenyl, allyl, alkenyloxy, alkenylamino,allyloxy, allylamino, furanyl, phenyl and benzyl groups.
 7. Thecomposition according to claim 2, wherein said silane crosslinker is amember selected from the group consisting of vinyltrimethoxysilane,vinyltriaminosilane, vinyltriamidosilane, vinyltrioximinosilane,vinyltris(methyl ethylketoximino)silane, vinyltriisopropenyloxysilane,vinyltriacetoxysilane, and combinations thereof.
 8. The compositionaccording to claim 1, further comprising (E) a third silicone fluid,said third silicone fluid comprised of at least one(meth)acryloxyalkyldialkoxy-terminated polyorganosiloxane.
 9. Thecomposition according to claim 8, wherein said third silicone fluid (E)is selected from the group consisting ofmethacryloxypropyldimethoxy-terminated polyorganosiloxane,acryloxypropyldimethoxy-terminated polyorganosiloxane and combinationsthereof.
 10. The composition according to claim 1, wherein the secondsilicone fluid is selected from the group consisting ofmethacryloxypropylsilyl-terminated silicone,acryloxypropylsilyl-terminated silicone and combinations thereof. 11.The composition according to claim 1, for use as a potting composition.12. The composition according to claim 1, wherein said silicone (ii)reactive with a (meth)acryloxy functionality of said silyl diacrylatecompound imparts moisture-curing to said composition.
 13. Thecomposition according to claim 12, wherein said moisture-curing isimparted due to the presence of a moiety selected from the groupconsisting of bydroxyl, enoloxy, amino, alkoxy, aryloxy, oxime,N,N-dialkylamino, N,N-dialkylaminoxy, N-alkylamido,O—C(CH₃)═CH₂,—S—C₃H₆Si(OCH₃)₃,—O—NH—C—(O)—H and combinations thereof.14. The composition according to claim 1, wherein the (meth)acryloxyalkyldialkoxy-terminated polyorganosiloxane (E) is a product ofthe reaction of an organopolysiloxane, having at least one endterminated with a silanol group, with a silane containing three alkoxygroups.
 15. The composition according to claim 8, wherein the(meth)acryloxyalkyl terminated polyorganosiloxane (E) is in accordancewith formula I below:

wherein R¹, R², R³, and R⁴ may be the same or different and aremonovalent hydrocarbon radicals having up to 10 carbon atoms (C₁₋₁₀) orhalo or cyano substituted hydrocarbon radicals; R³ may also bemonovalent heterohydrocarbon radical having up to 10 carbon atoms(C₁₋₁₀) wherein the hereto atoms are selected from halo atoms, O, N, andS; at least one R³ on a terminal end is a (meth)acryloxyalkly group; R⁵is alkyl (C₁₋₁₀) or alkoxy; n is an integer; a is 0, 1 or 2; b is 0, 1or 2; and a+b is 1 or
 2. 16. The composition according to claim 15,wherein n is from 1 to 1,200 such that the(meth)acryloxyalkyldialkyloxy-terminated polyorganosiloxane (E) has aviscosity from about 25 cps to about 2,500,000 cps at 25° C.
 17. Thecomposition according to claim 8, wherein R³ is a methacrylate-propylgroup, CH₂C(CH₃)—COOC₃H₆, R⁴ and R⁵ are methyl, and R¹ and R² are asdescribed in formula I above to give the following formula:

wherein MA is a methacryloxypropyl group, n is from 1 to 1,200 and c is0 or
 1. 18. The composition according to claim 1, wherein said firstsilicone fluid is present in amounts of about 5% to about 60% by weightof the composition.
 19. The composition according to claim 1, whereinsaid second silicone fluid is present in amounts of about 5% to about90% by weight of the composition.
 20. The composition according to claim1, wherein the photoinitiator is a member selected from the groupconsisting of benzophenone and substituted benzophenones, acetophenoneand substituted acetophenones, benzoin and its alkylesters, xanthone andsubstituted xanthones, and combinations thereof.
 21. The compositionaccording to claim 1, wherein the photoinitiator is a member selectedfrom the group consisting of diethoxyacetophenone, benzoin methyl ether,benzoin ethyl ether, benzoin isopropyl ether, diethoxyxanthone,chloro-thioxanthone, azo-bisisobutyronitrile, N-methyldiethanolaminebenzphenone, and combinations thereof.
 22. The compositionaccording to claim 1, wherein the photoinitiator is a member selectedfrom the group consisting of camphoroquinone peroxyester initiators,non-fluorene-carboxylic acid peroxyesters and combinations thereof. 23.A method of preparing the composition according to claim 1, the steps ofwhich include mixing said components to provide a blend under a dry airor nitrogen atmosphere.